Metallic acetylacetonates

The chemical structure of a typical divalent metal acetylacetonate, for which the abbreviation would be MCacac). These compounds are internally bonded ionically and complexed to oxygen at the same time. Thus, their intramolecular forces are very strong (they are stable), but their interraolecular forces are weak (they are volatile). 

Kaeriyama and Shimura [34] have reported the photoinitiation of polymerization of MMA and styrene by 12 metal acetylacetonate complex. These are Mn(acac)3, Mo02(acac)2, Al(acac)3, Cu(bzac)2, Mg(acac)2, Co(a-cac)2, Co(acac)3, Cr(acac)3, Zn(acac)2, Fe(acac)3, Ni(a-cac)2, and (Ti(acac)2) - TiCU. It was found that Mn(a-cac)3 and Co(acac)3 are the most efficient initiators. The intraredox reaction with production of acac radicals is proposed as a general route for the photodecomposition of these chelates. 

Metal acetylacetonates (M-ac.ac), also known as pentanedionates, are produced by reacting metals and acetyl acetone. They have the following chemical structure ... 

This is the most common route, the reagent being a metal compound/solvent combination. Typical conditions call for the metal salt (e.g., acetate) in a buffer system (e.g., NaOAc/AcOH) and a co-solvent such as chloroform. Generally the reaction mixture is refluxed until the metal complex spectrum (see Section 9.22.5.6 and Table 4) is fully developed. Metal acetylacetonates and metal phenoxides have also been employed. The topic has been reviewed in detail by Buchler,51 who has also summarized the history and classification of metal complexes of this series, and the mechanisms of metalation.52... 

The effectiveness of complexes metal-acetylacetonate with tris(l,l-dimethylethyl-4-methylphenyl) phosphite in their reaction with peroxyl radicals of styrene and tetralin (323 K) decreases in the row Co2+ > V02+ > Cr3+ > Fe2+ [88]. 

Ommen, J. G. van, K. Hoving, H. Bosch, A. J. van Hengstum and P. J. Gellings. 1983. The preparation of supported oxide catalysts by adsorption of metal acetylacetonates, M(AcAc)n on different supports. Z. Phys. Chemie Neue Folge 134 99-106. 

Table 4.10 Distribution Constants for Acetylacetone (HA) and Some Metal Acetylacetonates Between Various Organic Solvents and 1 M NaC104 at 25°C... 

Both monomers and polymers have been reported in the mass spectra of metal acetylacetonates (105, 106), depending on the nature of the metal, and its oxidation state different laboratories have reported conflicting results. Undergraduates in our freshman laboratory (107) recently discovered Cr2(acac)5 ions in the spectrum of Cr(acac)j but found that this dimer was removed if the sample was carefully purified, thus casting doubt on the purity of some of the previously reported (acac) derivatives showing dimers. 

Treatment of a series of metal acetylacetonates with the N-halogen suc-cinimides in boiling chloroform afforded the trihalogenated metal chelates in high yields. The use of bromine or iodine monochloride in buffered acetic acid also yielded the bromo- and iodochelates (7). 

Friedel-Crafts acylations of the metal acetylacetonate rings are much slower than the electrophilic substitutions described above, probably because of the considerable steric bulk at the reaction site. Furthermore, the strongly acidic conditions during the reaction and subsequent hydrolysis step give rise to considerable degradation, particularly in the case of the more sensitive chromium and cobalt chelates. This consideration places severe limitations on the reaction conditions that can be employed. 

Several of the unusual chemical properties of functional groups on metal acetylacetonate rings may be explained in terms of the considerable steric hindrance afforded the central carbon of the chelate ring by the flanking methyl groups. To examine this hypothesis the preparation of chelates of formyl acetone (XXXVIII) and malonaldehyde (XXXIX) was undertaken. 

TABLE III. Per Cent Exchange of Metal Acetylacetonates with C14-Labeled Acetylacetone... 

With trivatent metals, acetylacetone thus forms neutral tns complexes such as [Al(acac)3, [Tifacac),], (Crfacac),], and [Cofacac),]. As a result of resonance, the two M—O bonds in each of these complexes are equal in length, as are the two C—O and the two ring C—C bonds, giving a symmetric structure (only one ring shown) ... 

Metal acetylacetonates quench triplet species generated by flash photolysis of aromatic ketones and hydrocarbons.330-333 More recently, these reactions have been studied from a synthetic standpoint. Triplet state benzophenone sensitizes photoreduction of Cu(MeCOCHCOMe)2 by alcohols to give black, presumably polymeric, [Cu(MeCOCHCOMe)] . This reacts with Lewis bases to provide complexes of the type CuL2(MeCOCHCOMe) (L = bipyridyl/2, ethylenediamine/2, carbon monoxide, Ph3P). Disubstituted alkynes yield Cu(C2 R2 XMeCOCHCOMe) but terminal alkynes form CuQR acetylides.334 The bipyridyl complex of copper(I) acetylacetonate catalyzes the reduction of oxygen to water and the oxidation of primary and secondary alcohols to aldehydes and ketones.335... 

Only a small amount of research has been published dealing with the reactions of / -diketones with clean metal surfaces.513,514 The interaction of acetylacetone with iron and nickel films under ultra high vacuum conditions has been investigated. X-Ray photoelectron spectroscopy is a particularly useful analytical probe as data on gas phase metal acetylacetonates are available for comparison.515 On iron, dissociative adsorption giving acetylacetonate occurs at 90 K. This decomposes at about 290 K to form surface oxide, chemisorbed oxygen and a species considered to contain Fe—C bonds. 

Zrlv and HfIV porphyrins are prepared from metal acetylacetonates and porphyrin, but the product depends on the solvent and the work-up procedure.17 Mlv(Por)(acac)2, Mlv(Por)-(acac)(OPh) and Mlv(Por)(02CMe)2 are all interconvertible, and the additional ligands are on the same side of the porphyrin (Scheme 10). The acetato groups serve as bidentate ligands and the metal atom is centred in a distorted square antiprism.21 Zr(OEP)(02CMe)2 and Hf(0EP)(02CMe)2 are isodimensional with M—Npor x 2.26 A, M—O a 2.28 A and A(N4) x 1 A. 

Fig.4.33. Separation of six metal acetylacetonates (see text for details). (From ref. 60 with permission of the American Chemical Society, Washington.)...

The metal chelates are usually prepared from acetylacetone or trifluoroacetylacetone and are dissolved in a small quantity of stationary phase for the injection and separation. The UV absorbance of the derivatives is measured at 310 nm in a monitor equipped with a microflow cell. The separation of six metal acetylacetonates is shown in Fig.4.33 (column, SO cm X 2.7 mm I.D. particle diameter, 5-10 /am flow-rate, 1.8 mm/sec). 

The small peaks that are found 597 cm-1 to higher energy from the sharp peaks in the molecular beam spectrum are assigned to a quantum of the PtO totally symmetric stretch. In the Raman spectrum of Pt(hfacac)2 and Pt(acac)2 the PtO stretch occurs at 635 cm-1 and 485 cm-1, respectively [35]. It occurs between 420 cm -1 and 500 cm -1 in a series of metal acetylacetonates complexes [36]. The band in the 23(XX)cm-1 region of the molecular beam spectrum is overlapped by components of the ligand field band. 

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